// Physical memory allocator, intended to allocate
// memory for user processes, kernel stacks, page table pages,
// and pipe buffers. Allocates 4096-byte pages.

#include "types.h"
#include "defs.h"
#include "param.h"
#include "mmu.h"
#include "spinlock.h"

int maxAvailablePages = 0;

struct run {
  struct run *next;
};

struct {
  struct spinlock lock;
  struct run *freelist;
  int available_pages;
} kmem;

// Initialize free list of physical pages.
void
kinit(void)
{
  extern char end[];

  initlock(&kmem.lock, "kmem");
  kmem.available_pages = 0;
  char *p = (char*)PGROUNDUP((uint)end);
  for( ; p + PGSIZE - 1 < (char*) PHYSTOP; p += PGSIZE){
    kfree(p);
  }
  maxAvailablePages = kmem.available_pages;
}

// Free the page of physical memory pointed at by v,
// which normally should have been returned by a
// call to kalloc().  (The exception is when
// initializing the allocator; see kinit above.)
void
kfree(char *v)
{
  struct run *r;

  if(((uint) v) % PGSIZE || (uint)v < 1024*1024 || (uint)v >= PHYSTOP)
    panic("kfree");

  // Fill with junk to catch dangling refs.
  //This will cause code that uses memory after freeing it (uses "dangling references")
  //to read garbage instead of the old valid contents;
  memset(v, 1, PGSIZE);

  acquire(&kmem.lock);
  r = (struct run *) v;
  r->next = kmem.freelist;
  kmem.freelist = r;
  kmem.available_pages++;
  release(&kmem.lock);
}

// Allocate one 4096-byte page of physical memory.
// Returns a pointer that the kernel can use.
// Returns 0 if the memory cannot be allocated.
char*
kalloc()
{
  struct run *r;

  acquire(&kmem.lock);
  r = kmem.freelist;
  if(r){
    kmem.freelist = r->next;
    kmem.available_pages--;
  }
  release(&kmem.lock);
  return (char*) r;
}

int freePagesPercentage(){
	int percentage = 0;
	acquire(&kmem.lock);
	percentage =  ((double)kmem.available_pages/(double)maxAvailablePages)*100;
	release(&kmem.lock);
	return percentage;
}
